Testing Hadronic Interactions at Ultrahigh Energies with Air Showers Measured by the Pierre Auger Observatory

Ultrahigh energy cosmic ray air showers probe particle physics at energies beyond the reach ofaccelerators. Here we introduce a new method to test hadronic interaction models without relying on theabsolute energy calibration, and apply it to events with primary energy 6–16 EeV (E_CM = 110–170 TeV),whose longitudinal development and lateral distribution were simultaneously measured by the Pierre AugerObservatory. The average hadronic shower is 1.33 +/- 0.16 (1.61 +/- 0.21) times larger than predicted usingthe leading LHC-tuned models EPOS-LHC (QGSJetII-04), with a corresponding excess of muons